The pictures are kind of self-explanatory ;)
Basically you mount this to your dustpan so that after sweeping, you can run your broom's bristles over the "teeth" to wipe off the remaining stuck-on debris.
I would recommend printing in ABS with 100% infill, for strength and flexibility. I had to bend mine a little for it to fit. It might have otherwise snapped with a low infill (or using PLA).
I used .3 layer height, with a raft.
The length is about 7 1/2 inches x 1 1/2 inch in depth. Scale as necessary depending on your dustpan's size.
Three holes were added for the screw mounts, but you might have to drill them slightly larger (not too large though or it will crack). I used screws with a washer and bolt for added security, rather than just a screw by itself.